First, I'd disagree about Kursk. The German offensive failed because they attacked into to prepared Russian defensive positions. The Russians knew exactly where they going to attack, thanks to their own intelligence as well as reports from an agent they had planted in Bletchley Park. The Germans were stopped by Soviet minefields and prepared artillery positions. Then the Russians launched a massive armored counter attack. It was a classic case of German quality vs Russian quantity. The German panthers and tigers killed many more Russian tanks than they lost, but the Russians could lose dozens of tanks and they were easily replaced, each one the Germans lost was a catastrophe.

And I still maintain once the war in the east started a cross channel invasion of Britain was impossible, German air power was needed in Russia and north Africa. Without air superiority it would have been a disaster. In the close confines of the channel the U boats would have been easy meat. The British had made advances in anti submarine warfare, and really Hitler never was that enthusiastic about fighting England. His twisted racial ideas had always led him east, against the Slavs. He considered the British the racial equals of the Germans.